Question: Solve for $x$ and $y$ using substitution. ${4x+y = 7}$ ${y = -x-2}$
Solution: Since $y$ has already been solved for, substitute $-x-2$ for $y$ in the first equation. ${4x + }{(-x-2)}{= 7}$ Simplify and solve for $x$ $4x-x - 2 = 7$ $3x-2 = 7$ $3x-2{+2} = 7{+2}$ $3x = 9$ $\dfrac{3x}{{3}} = \dfrac{9}{{3}}$ ${x = 3}$ Now that you know ${x = 3}$ , plug it back into $\thinspace {y = -x-2}\thinspace$ to find $y$ ${y = -}{(3)}{ - 2}$ $y = -3 - 2$ $y = -5$ You can also plug ${x = 3}$ into $\thinspace {4x+y = 7}\thinspace$ and get the same answer for $y$ : ${4}{(3)}{ + y = 7}$ ${y = -5}$